With the miniaturized, portable, ultra-thin, multi-media and low cost-oriented development of electronic products such as mobile phones, laptops, etc., high-density, high-performance, high-reliability and low-cost package forms and the assembly technology have been developed rapidly. Compared with expensive packages such as BGA and the like, in recent years, the novel package technology has developed rapidly (that is, QFN package (Quad Flat Non-lead Package)). As they have the advantages of good thermal and electrical performance, small size, low cost, high productivity, etc., a new revolution in the field of microelectronics packaging technology is introduced.
FIG. 1A is a bottom view of conventional QFN package. FIG. 1B shows a cross-sectional view of conventional QFN package taken along line I-Í of FIG. 1A. Conventional QFN package 100 comprises lead frame 11, plastic mold material 12, adhesive layer 13, IC chip 14 and metal wires 15, wherein lead frame 11 comprises chip pad 111 and leads 112 arrayed around chip pad 111. IC chip 14 is fixed on chip pad 111 through adhesive material 13. IC chip 14 and the leads 112 arrayed around are in electrical communication through metal wires 15. Plastic mold material 12 encapsulates IC chip 14, metal wires 15 and lead frame 11 to protect and support them. Chip pad 111 and leads 112 are exposed at the lower surface of plastic mold material 12. Leads 112 are welded on a circuit board such as PCB and the like through solder to realize the electrical connection with external circuits. Chip pad 111 is welded on a circuit board such as PCB and the like through solder. As a result, there is a direct heat dissipation channel to effectively release the heat generated by IC chip 14. Compared with TSOP and SOIC packages, QFN package does not have a gull wing-shaped lead and has a short conductive path, low self-inductance coefficient and low impedance, thus providing sound electrical performance and meeting high-speed or microwave application requirement.
With the improved integration and enhanced functions of IC, the I/O number of IC is increased, and the I/O number of leads of electronic package is correspondingly increased. The package form is gradually developed from two-dimensional package form to three-dimensional package form with better integration. The conventional QFN package 100 is in the typical two-dimensional package form. Just only a single row of leads 112 are arrayed around chip pad 111, thus limiting the number of leads 112 and not meeting the requirements of IC with high density and more I/Os.
The lead frame 11 of conventional QFN package 100 is not effectively interlocked with plastic mold material 12, resulting in poor adhesion between lead frame 11 and plastic mold material 12, which may easily cause delamination failure, and even chip pad 111 and leads 112 falling off. Furthermore, moisture may not be effectively prevented from diffusing into inside along the interface between lead frame 11 and plastic mold material 12. During the molding process of conventional QFN package 100, an adhesive tape is required to be pasted on the bottom of lead frame 11 in advance to prevent overflow problem. After molding process, the adhesive tape removing, the plastic mold material flash trimming and cleaning processes are required, which thus increases the manufacturing cost. During the sawing process of conventional QFN package 100, a blade saws the metal of lead frame 11 as well as plastic mold material 12, which results in lower efficiency, short blade life, and metal burrs problem. Therefore, in order to break through the bottleneck of the low density, to improve reliability, and to reduce manufacturing cost of conventional QFN package, there is an urgent need to develop a three-dimensional package based on QFN package and a manufacturing method thereof with high reliability, low cost, and high density.